1. Field of the Invention
The present invention relates to a process for separating a number of sheets into groups, and an adhesive composition for use therein.
2. Description of the Prior Art
Processes for separating a number of sheets such as a pressure sensitive copying paper into groups are described in U.S. Pat. Nos. 2,711,375; 2,712,507; 2,730,456; 2,730,457; 3,418,250; 3,432,327; etc., for example, and adhesive compositions for use therein are described in detail in Japanese Patent Publication No. 35696/1971, Japanese Patent Publication Nos. 40464/1973 and 7634/1975, etc.
In the prior art methods, gelatin, gelatin derivatives, gelatin decomposition products, or mixtures thereof with aqueous emulsions of a resin, i.e., a polymer latex, are used as an adhesive component.
However, since gelatins tend to degrade, and the viscosity thereof varies greatly depending upon the temperature, adhesive containing gelatins are not satisfactory in storage stability, adhesiveness, and separability. In the present specification, the term "separability" designates that the sheets are separated into groups. Thus, when the separability is good, the sheets are easily separated into groups, and when the separability is poor the sheets are difficult to separate into groups. The latexes which are added for the purpose of improving the adhesiveness, decrease the separability, and thus it is desired that the adhesives containing the latexes are further improved.